Hello!
I’m struggling to correct this but with no luck 
I’ve tried with all the sets (lights, darks, flats, bias), and with only lights. This thing is not going anywhere…
Also tried first to load the RAW files to PS, perform a lens correction, export to tiff and then again in Siril. No luck either…
Is there any tool that can help me with that?
PS. The pictures were taken with a Canon77D and Canon 55-250mm (135mm exactly)
.In astrophotography, the only way to remove vignetting is to divide by a flat field image.
But this image must be done right after the session using the same optical path.
If your focale changed just a little, no way to shoot a correct flat field.
Sorry but I forgot to upload the a picture before 
I’ve already tried it but I can’t see any change
Yes but maybe your flat is not correct.
It is not that easy, especially with zoom lenses.
Thank you,
I’ll certainly retry it from scratch, cause it’s really drive me crazy. I can’t proceed with the post with that there
I’ve experienced this same issue when shooting with my DSLR and telephoto lens. I found that covering the viewfinder with black gaffers tape worked great. Doesn’t really help with the edge vignetting but the big oval disappeared.
